Develop Reference

JSF commandButton action is invoked from javascript even if false is returned [duplicate]

Hey there is a link in my program as shown and onclick it calls the function clearform as shown:
Html Code:
<a class="button" href="Cancel" style="left: 55%;" onclick="clearForm()">Cancel</a>
JavaScript Code:
function clearForm(){
document.getElementById("subjectName").value = "";
return false;
}
return false is not working in this code. actually the first line of the function executed successfully but the return false was failed. I mean page is redirected to url "Cancel".

Change your code as
<a class="button" href="Cancel" onclick="return clearForm()">Cancel</a>

Your problem is you need to return the Boolean.
But, drop all that...
Attach your event unobtrusively...
element.onclick = clearForm;
Use preventDefault(). It is the modern way of acheiving that.
function clearForm(event) {
event.preventDefault();
}

<a class="button" href="Cancel" style="left: 55%;" onclick="clearForm();return false;">Cancel</a>
should work

Please note that if there is a bug or error in clearForm() then "return false" will NOT stop the anchor action and your browser will try to link to the href "Cancel". Here is the logic:
User clicks on anchor
onClick fires clearForm()
There is an error in clearForm() so Javascript crashes and stops all code execution.
return false is never fired because Javascript has already stopped.
If you are relying on a third party JavaScript API (I was using code supplied by Recyclebank to spawn a popup), and the third party API makes an update that breaks the JavaScript, then you'll have problems.
The following will stop the link under normal conditions and error conditions.
<a class="button" href="javascript:;" style="left: 55%;" onclick="clearForm();return false;">Cancel</a>

The return false; somehow needs to be right at the front.
(In ALL situations I've dealt with over the past months - may or may not be a bug).
Like this: onclick="return false; clearForm();"
Besides that, as mentioned by others as well, you need to return it from the onclick, not just from the function.
In your case: onclick="return clearForm()".

Keep in mind that some browser extensions may interfere with proper operation of links. For example, I ran into a situation where someone had both AdBlock Plus and Ghostery enabled. Clicking a simple 'a' tag with an 'onclick="return SomeFunction();"' attribute (the function returned false) caused the browser to treat the click as a page transition and went to a blank page and the loading indicator just kept spinning. Disabling those browser extensions cleared up the problem.
Including this as an answer because this was the first page I landed on from Google.

jQuery dialog call redirecting page

I'm using the jQuery dialog plugin.
The dialog div is set up (but not opened) on page load:
$(document).ready(function(){
$('#foo').dialog({autoOpen:false});
});
Then a hyperlink is supposed to open the dialog:
Show dialogue box
But this opens the dialog then a fraction later redirects to a page with the URL javascript:$('#foo').dialog('open');!
I have tried returning false:
Show dialogue box
But then the link doesn't respond at all when I click on it.
I know this must be to do with one of JavaScript's infamous subtleties but I can't work it out.
Can anyone help?

Then a hyperlink is supposed to open the dialog:
Show dialogue box
But this opens the dialog then a fraction later redirects to a page with the URL javascript:$('#foo').dialog('open');!
That shouldn't be happening. The pseudo-protocol javascript: doesn't involve a page load, and certainly not one via HTTP. I don't recommend it (I'd use jQuery's click handler instead), but it should work.
I have tried returning false:
...
But then the link doesn't respond at all when I click on it.
That also shouldn't be happening.
Your code as quoted is fine (works here, for instance: http://jsbin.com/inixa5), so the problem must lie in some other part of the page.
Update: Okay, that's weird, IE6 and IE7 didn't like that; I think it's because dialog returns a value. You can get around that either by wrapping up your call to open the dialog in a function and doesn't explicitly return anything:
Click Me
<script>
$("#foo").dialog({autoOpen: false});
function showDialog(selector) {
$(selector).dialog('open');
}
</script>
Or (and this is mega-hacky) by making sure the last expression in the javascript: block is undefined:
Click Me
<script>
$("#foo").dialog({autoOpen: false});
</script>
Or by using onclick:
Click Me
<script>
$("#foo").dialog({autoOpen: false});
</script>
But in any case, strongly recommend hooking things up with a DOM2 style event handler:
<a href="#" name='openSesame'>Click Me</a>
<script>
// This _can_ be immediately after the anchor, but I'd put it in
// a separate, since .js file for the page that you load just before
// the closing body tag.
$("#foo").dialog({autoOpen: false});
$("a[name=openSesame]").click(function() {
$("#foo").dialog('open');
return false;
});
</script>
Live example (Obviously, you can use any selector that makes sense, you don't have to give the anchor a name [or id].)
One of the nice things about this is that you can then have the anchor take the user somewhere meaningful and/or useful if JavaScript is disabled (something called progressive enhancement).

Change the link to:
<a href="javascript:void(0)" onclick="$('#foo').dialog('open')">
Show dialogue box
</a>
Best avoid putting javascript in the href.
Even better would be giving it a class and than adding a click event to it through jquery.

href="javascript:" vs. href="javascript:void(0)"

Our web app is rendered totally on the browser.The server only talks to the browser through JSON messaging.
As a result, we only need a single page for the app and mostly all the <a> tags do not have a real href pointing to other pages.
In my quest of removing unnecessary things I was wondering if I can get rid of the zillions of void(0) we have in our code, as they seem useless:
<a onclick="fn()">Does not appear as a link, because there's no href</a>
fn is called
fn is called too!
Does anybody knows if using href="javascript:" can cause a problem?
It works even on IE7...
Please don't spend your valuable time to tell me inline javascript is bad, as this is generated by a template engine :)

It does not cause problems but it's a trick to do the same as PreventDefault
when you're way down in the page and an anchor as:
click here
you will jump to the top and the URL will have the anchor # as well, to avoid this we simply return false; or use javascript:void(0);
regarding your examples
<a onclick="fn()">Does not appear as a link, because there's no href</a>
just do a {text-decoration:underline;} and you will have "link a-like"
fn is called
fn is called too!
it's ok, but in your function at the end, just return false; to prevent the default behavior, you don't need to do anything more.

When using javascript: in navigation the return value of the executed script, if there is one, becomes the content of a new document which is displayed in the browser. The void operator in JavaScript causes the return value of the expression following it to return undefined, which prevents this action from happening. You can try it yourself, copy the following into the address bar and press return:
javascript:"hello"
The result is a new page with only the word "hello". Now change it to:
javascript:void "hello"
...nothing happens.
When you write javascript: on its own there's no script being executed, so the result of that script execution is also undefined, so the browser does nothing. This makes the following more or less equivalent:
javascript:undefined;
javascript:void 0;
javascript:
With the exception that undefined can be overridden by declaring a variable with the same name. Use of void 0 is generally pointless, and it's basically been whittled down from void functionThatReturnsSomething().
As others have mentioned, it's better still to use return false; in the click handler than use the javascript: protocol.

Using 'javascript:void 0' will do cause problem in IE
when you click the link, it will trigger onbeforeunload event of window !
<!doctype html>
<html>
<head>
</head>
<body>
<a href="javascript:void(0);" >Click me!</a>
<script>
window.onbeforeunload = function() {
alert( 'oops!' );
};
</script>
</body>
</html>

This method seems ok in all browsers, if you set the onclick with a jQuery event:
Click me!
As said before, href="#" with change the url hash and can trigger data re/load if you use a History (or ba-bbq) JS plugin.

you could make them all #'s.
You would then need to add return false; to the end of any function that is called onclick of the anchor to not have the page jump up to the top.

I usually do not use any href and change the aspect with css, making them seems link. Thus you do not have to worry about link effect at all, except for the event handler of your application
a {
text-recoration: underline;
cursor: pointer;
}

javascript:void(0); --> this executes void function and returns undefined. This could have issues with IE.
javascript:; --> this does nothing. safest to create dead links.
'#' --> this means pointing to same DOM, it will reload the page on click.

Why have all the click events as a href links?
If instead you use span tags with :hover CSS and the appropriate onclick events, this will get around the issue completely.

HTML anchor link with no scroll or jump

I have various links which all have unique id's that are "pseudo-anchors." I want them to affect the url hash value and the click magic is all handled by some mootools code. However, when I click on the links they scroll to themselves (or to the top in one case). I don't want to scroll anywhere, but also need my javascript to execute and to have the hash value in the url update.
Simulated sample code:
button 1
button 2
Home
So if you were to click on the "button 1" link, the url could be http://example.com/foo.php#button1
Does anyone have any ideas for this? Simply having some javascript return void kills the scrolling but also kills my javascript (though I could probably work around that with an onclick) but more importantly, prevents the hash value in the url to change.

The whole point of an anchor link is to scroll a page to a particular point. So if you don't want that to happen, you need to attach an onclick handler and return false. Even just adding it as an attribute should work:
button 1
A side of effect of the above is that the URL itself won't change, since returning false will cancel the event. So since you want the URL to actually change, you can set the window.location.hash variable to the value that you want (that is the only property of the URL that you can change without the browser forcing a reload). You can probably attach an event handler and call something like window.location.hash = this.id though I'm not sure how mootools handles events.
(Also you need all of the IDs to be unique)

You can use the code below to avoid scrolling:
linktxt

I'm probably missing something, but why not just give them different IDs?
button 1
button 2
Home
Or whatever convention you'd prefer.

Also, preventDefault
$(your-selector).click(function (event) {
event.preventDefault();
//rest of your code here
}

I found the solution. Here I save an old location from calling href
and restore it after scrolling
<script language="JavaScript" type="text/javascript">
<!--
function keepLocation(oldOffset) {
if (window.pageYOffset!= null){
st=oldOffset;
}
if (document.body.scrollWidth!= null){
st=oldOffset;
}
setTimeout('window.scrollTo(0,st)',10);
}
//-->
</script>
and in body of page
<a href="#tab1" onclick="keepLocation(window.pageYOffset);" >Item</a>
Thanks to sitepoint

An easier way would probably be to add it as a GET. That is, http://example.com/foo.php?q=#button1 instead of http://example.com/foo.php#button1
This won't have any effect on how the page is displayed (unless you want it to), and most scripting languages already have tools in place to easily (and safely) read the data.

Well here we are 7 years after this answer was published and I found a different way to make it work: just point the window.location.hash to a non-existent anchor! It doesn't work for <a>s but works perfectly in <div>s.
<div onclick="window.location.hash = '#NonExistentAnchor';">button 1</div>
Worked fine in Chrome 56, Firefox 52 and Edge (IE?) 38. Another good point is that this doesn't produce any console errors or warnings.
Hope it helps somebody besides me.

There is a solution without any JavaScript at all:
I will not jump to the top

Use
button 1
where
function setHash(hash) {
event.preventDefault();
history.pushState(null, null, "#"+hash);
}
event.preventDefault() stops browser from what it normally would do on clicking, and history.pushState adds to the sessions history stack.
For further discussion, see here and here

JavaScript - href vs onclick for callback function on Hyperlink

I want to run a simple JavaScript function on a click without any redirection.
Is there any difference or benefit between putting the JavaScript call in the href attribute (like this):
....
vs. putting it in the onclick attribute (binding it to the onclick event)?

bad:
<a id="myLink" href="javascript:MyFunction();">link text</a>
good:
<a id="myLink" href="#" onclick="MyFunction();">link text</a>
better:
<a id="myLink" href="#" onclick="MyFunction();return false;">link text</a>
even better 1:
<a id="myLink" title="Click to do something"
href="#" onclick="MyFunction();return false;">link text</a>
even better 2:
<a id="myLink" title="Click to do something"
href="PleaseEnableJavascript.html" onclick="MyFunction();return false;">link text</a>
Why better? because return false will prevent browser from following the link
best:
Use jQuery or other similar framework to attach onclick handler by element's ID.
$('#myLink').click(function(){ MyFunction(); return false; });

Putting the onclick within the href would offend those who believe strongly in separation of content from behavior/action. The argument is that your html content should remain focused solely on content, not on presentation or behavior.
The typical path these days is to use a javascript library (eg. jquery) and create an event handler using that library. It would look something like:
$('a').click( function(e) {e.preventDefault(); /*your_code_here;*/ return false; } );

In terms of javascript, one difference is that the this keyword in the onclick handler will refer to the DOM element whose onclick attribute it is (in this case the <a> element), whereas this in the href attribute will refer to the window object.
In terms of presentation, if an href attribute is absent from a link (i.e. <a onclick="[...]">) then, by default, browsers will display the text cursor (and not the often-desired pointer cursor) since it is treating the <a> as an anchor, and not a link.
In terms of behavior, when specifying an action by navigation via href, the browser will typically support opening that href in a separate window using either a shortcut or context menu. This is not possible when specifying an action only via onclick.
However, if you're asking what is the best way to get dynamic action from the click of a DOM object, then attaching an event using javascript separate from the content of the document is the best way to go. You could do this in a number of ways. A common way is to use a javascript library like jQuery to bind an event:
<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<a id="link" href="http://example.com/action">link text</a>
<script type="text/javascript">
$('a#link').click(function(){ /* ... action ... */ })
</script>

EDITOR WARNING: See the comments, the use of 'nohref' is incorrect in this answer.
I use
Click <a nohref style="cursor:pointer;color:blue;text-decoration:underline"
onClick="alert('Hello World')">HERE</a>
A long way around but it gets the job done. use an A style to simplify
then it becomes:
<style> A {cursor:pointer;color:blue;text-decoration:underline; } </style>
<a nohref onClick="alert('Hello World')">HERE</a>

The top answer is a very bad practice, one should never ever link to an empty hash as it can create problems down the road.
Best is to bind an event handler to the element as numerous other people have stated, however, do stuff works perfectly in every modern browser, and I use it extensively when rendering templates to avoid having to rebind for each instance. In some cases, this approach offers better performance. YMMV
Another interesting tid-bit....
onclick & href have different behaviors when calling javascript directly.
onclick will pass this context correctly, whereas href won't, or in other words no context won't work, whereas <a onclick="javascript:doStuff(this)">no context</a> will.
Yes, I omitted the href. While that doesn't follow the spec, it will work in all browsers, although, ideally it should include a href="javascript:void(0);" for good measure

the best way to do this is with:
The problem is that this WILL add a hash (#) to the end of the page's URL in the browser, thus requiring the user to click the back button twice to go to the page before yours. Considering this, you need to add some code to stop event propagation. Most javascript toolkits will already have a function for this. For example, the dojo toolkit uses
dojo.stopEvent(event);
to do so.

In addition to all here, the href is shown on browser's status bar, and onclick not. I think it's not user friendly to show javascript code there.

This works
Click Here

Having javascript: in any attribute that isn't specifically for scripting is an outdated method of HTML. While technically it works, you're still assigning javascript properties to a non-script attribute, which isn't good practice. It can even fail on old browsers, or even some modern ones (a googled forum post seemd to indicate that Opera does not like 'javascript:' urls).
A better practice would be the second way, to put your javascript into the onclick attribute, which is ignored if no scripting functionality is available. Place a valid URL in the href field (commonly '#') for fallback for those who do not have javascript.

it worked for me using this line of code:
<a id="LinkTest" title="Any Title" href="#" onclick="Function(); return false; ">text</a>

First, having the url in href is best because it allows users to copy links, open in another tab, etc.
In some cases (e.g. sites with frequent HTML changes) it is not practical to bind links every time there is an update.
Typical Bind Method
Normal link:
<a href="https://www.google.com/">Google<a/>
And something like this for JS:
$("a").click(function (e) {
e.preventDefault();
var href = $(this).attr("href");
window.open(href);
return false;
});
The benefits of this method are clean separation of markup and behavior and doesn't have to repeat the function calls in every link.
No Bind Method
If you don't want to bind every time, however, you can use onclick and pass in the element and event, e.g.:
Google
And this for JS:
function Handler(self, e) {
e.preventDefault();
var href = $(self).attr("href");
window.open(href);
return false;
}
The benefit to this method is that you can load in new links (e.g. via AJAX) whenever you want without having to worry about binding every time.

Personally, I find putting javascript calls in the HREF tag annoying. I usually don't really pay attention to whether or not something is a javascript link or not, and often times want to open things in a new window. When I try doing this with one of these types of links, I get a blank page with nothing on it and javascript in my location bar. However, this is sidestepped a bit by using an onlick.

The most upvoted answer is obsolete today
I would recommend the exact opposite, see step by step with reasons:
good:
<a id="myLink" href="javascript:MyFunction();">link text</a>
It depends, might be good, because crawlers follows href targets and if there is any meaningful content produced by MyFunction() (dynamic link), it is followed more likely than in the click event, which may have multiple or none listeners.
bad:
<a id="myLink" href="#" onclick="MyFunction();">link text</a>
# means meaningless link, crawlers are often interested only in first x links, so it can prevent them to follow some meaningful links later in the page.
worse:
<a id="myLink" href="#" onclick="MyFunction();return false;">link text</a>
Same as previous plus return false prevents following the link. If some other scripts want to add another listener and update the target (say to redirect via proxy), they can't without modifying the onclick (okay, it's just a minor setback as such use cases are rather theoretical).
worst:
Use jQuery or other similar framework to attach onclick handler by element's ID.
$('#myLink').click(function(){ MyFunction(); return false; });
jQuery is outdated in 2020+ and should not be used in new projects.
Events in href
The href attribute handler doesn't get the event object, so the handler doesn't implicitly see which link was the source. You can add it in onclick handler, which fires before the href is followed:
<a href="javascript:my_function(event2)" onclick="event2=event">
JS based link
</a>
<script>
function my_function(e) {
console.log(e.target); // the source of the click
if(something) location.href = ...; // dynamic link
}
</script>

One more thing that I noticed when using "href" with javascript:
The script in "href" attribute won't be executed if the time difference between 2 clicks was quite short.
For example, try to run following example and double click (fast!) on each link.
The first link will be executed only once.
The second link will be executed twice.
<script>
function myFunc() {
var s = 0;
for (var i=0; i<100000; i++) {
s+=i;
}
console.log(s);
}
</script>
href
onclick
Reproduced in Chrome (double click) and IE11 (with triple click).
In Chrome if you click fast enough you can make 10 clicks and have only 1 function execution.
Firefox works ok.

<hr>
<h3 class="form-signin-heading"><i class="icon-edit"></i> Register</h3>
<button data-placement="top" id="signin_student" onclick="window.location='signup_student.php'" id="btn_student" name="login" class="btn btn-info" type="submit">Student</button>
<div class="pull-right">
<button data-placement="top" id="signin_teacher" onclick="window.location='guru/signup_teacher.php'" name="login" class="btn btn-info" type="submit">Teacher</button>
</div>
</div>
<script type="text/javascript">
$(document).ready(function(){
$('#signin_student').tooltip('show'); $('#signin_student').tooltip('hide');
});
</script>
<script type="text/javascript">
$(document).ready(function(){
$('#signin_teacher').tooltip('show'); $('#signin_teacher').tooltip('hide');
});
</script>

I experienced that the javascript: hrefs did not work when the page was embedded in Outlook's webpage feature where a mail folder is set to instead show an url

click here

I cant belive that +13 years later, all of these answers are semantically incorrect! An anchor element <a>:
...with its href attribute, creates a hyperlink to web pages, files, email addresses, locations in the same page, or anything else a URL can address.
Content within each should indicate the link's destination. If the href attribute is present, pressing the enter key while focused on the element will activate it.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a
Therefore, using an href= for javascript is bad practice and poor web semantics. You should rather be using an onclick= event handler attribute on a button element, as:
The HTML element is an interactive element activated by a user with a mouse, keyboard, finger, voice command, or other assistive technology. Once activated, it then performs a programmable action, such as submitting a form or opening a dialog.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/button
and the event handler onclick=:
All event handler attributes accept a string. The string will be used to synthesize a JavaScript function like function name(/args/) {body}, where name is the attribute's name, and body is the attribute's value.
https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes#event_handler_attributes
As you are not navigating to a URL or a Link destination, but rather triggering a Javascript function the correct way to do this is to use onclick. And if you need the style of an anchor tag on a button, just use CSS.
The bottom line is: just because you can do it doesn't mean you should.

This works as well
<a (click)='myFunc()'>Click Here </a>
(onclick) did not work for me in an Angular project with bootstrap.